In the area between the 30 and 40 m isobaths, just north of the Netherlands, a transition from Channel water to central North Sea water is found. Observations obtained in May and June 1986 show a predominantly along-isobath directed sub-tidal current. In the vertical cross-isobath plane a quasi-permanent upwelling zone overlying the steepest bottom slope is inferred from observed cross-isobath currents. In the same area Creutzberg (1985) observed a persistent chlorophyll a (chl a) maximum. Our observations show a chl a maximum extending from the bottom towards the pycnocline over a larger area in cross-isobath direction and with larger amounts of chl a than found by Creutzberg(1985). This chl a maximum is found above a zone of large amounts of benthic particulate organic carbon. The observed chl a distributions are compared with current and density observations via an advection-diffusion equation. Only rough estimates of the terms in this equation are obtained, which indicates that a balance between vertical advection and mixing, i.e. local generation, is most probable. The chl a distribution gives no evidence for an upwelling zone.